Conventionally, it is known that when wind turbine blades of a wind turbine generator receive wind and a rotor having the wind turbine blades rotates, an eccentric load is applied to a spindle system that rotates via the rotor and thus torsional vibration occurs. Therefore, a method for repressing the torsional vibration is considered.
For example, Patent Document 1 proposes a technique for detecting a torsional vibration component of a shaft system between a generator and wind turbine blades based on a change in a rotational speed of the generator and adjusting an electric current according to the torsional vibration component so as to repress the torsional vibration.